It is known to harden and produce steel components by heating a flat blank to an austenitization temperature, forming it, and then rapidly cooling it.
It is also known to heat already cold-formed components and then to cool and harden them in a tool that corresponds to the final shape of the component.
To obtain hardened components with regions of different hardnesses, it is among other things known to produce the components from laser-welded blanks, with the laser-welded blanks being composed of steels of different qualities and hardenabilities. A steel that can be hardened through a corresponding temperature increase is thus situated adjacent to a steel that either cannot be hardened at these temperatures, or is not hardenable in general.
DE 197 43 802 C2 has disclosed a method for producing a metallic formed component in which the metallic formed component is intended to have regions with a higher ductility; the formed component is composed of a hardenable steel and in a first step, partial regions of a blank are brought to a temperature of 600° C. to 900° C. in a period of less than 30 seconds, after which the heat-treated blank is formed into the formed component in a pressing tool and then the formed component is cooled in the pressing tool, thus partially hardening it.
In another embodiment described in this prior publication, a formed component is first homogenously heated to a temperature that is necessary for hardening and then the blank undergoes its final forming in the pressing tool, turning it into the formed component. The required hardening takes place in the pressing tool. The homogeneously hardened component is then placed onto a conveyor and oriented in position by holding devices. On this conveyor, the formed components pass through a heating device in which the regions that are to have a higher ductility are brought to a temperature of 600° C. to 800° C. in an extremely short time by an inductor and are then cooled slowly enough that a renewed hardening does not occur and instead, these parts are in turn ductile. This method has the disadvantage that it requires multiple steps and is also energy intensive.
DE 200 14 361 U1 has disclosed a B-pillar for a motor vehicle, which is composed of a longitudinal profile of steel, in which the longitudinal profile is intended to have a first longitudinal section, which has a predominantly martensitic material structure and a strength of greater than 1,400 N/mm2, and a second longitudinal section, which has a higher ductility and a predominantly ferritic/pearlitic material structure and a strength of less than 850 N/mm2. To establish these different regions, it is known from this prior publication to insulate the longitudinal profile in the regions in which the longitudinal profile is to remain soft, to protect them from the heat of the furnace by placing insulating elements so that they encompass and cover the profile. As a result, these regions are supposed to experience no significant heating so that the total temperature increase in these sections is significantly below the austenitization temperature.
In another embodiment, the forming blank is first completely and homogeneously heated to an austenitization temperature and during the transfer or transport of the blank into the hardening tool, is brought to a temperature well below the austenitization temperature through targeted, not too abrupt cooling, so that no purely martensitic structure is produced during the hot forming. This method has the disadvantage that the targeted cooling of a blank or preformed component increases cycle times and requires additional processing steps. With an insulation from the heat of the furnace, it is disadvantageous that setting the insulation into place and removing it afterward entail additional steps that increase the cycle time and increase process costs.
EP 0 816 520 B1 has disclosed a press-hardened component and a method for the hardening thereof. This component is intended to include hardened and unhardened regions and the method uses an inductor to harden the component or profile by heating the component at least partway to an austenitization temperature and after being treated by the inductor, the component is conveyed to a cooling device, for example equipped with a water jet, which performs the rapid cooling necessary for hardening. Experiments have shown that this method is very expensive and results in extremely protracted cycle times; experiments have also shown that this method results in extremely powerful distortion of components. This is also the reason that this method is not used in actual practice.
The object of the invention is to create a method for producing partially hardened steel components which is simple and economically feasible while achieving high process reliability and favorably predictable hardness values in different regions.